You will definitely need to stop the service that is currently using port 80 if you want Apache to use port 80. You need to find out which service is still using port 80, "System" sounds too generic to be the right service to stop. Have you tried rebooting after uninstalling IIS?

Alternatively you can change Apache's port to something unused, for example 8080. Then when accessing your Apache server specify the port like this: http://localhost:8080/

I just rebooted, and when I opened the Xampp control panel and clicked start for Apache, it said Apache started [Port 80], as it always has, but now it says running in green! But when click the admin button, it goes to localhost and says not found
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Pat NeedhamOct 12 '11 at 23:40

As the name implies, it is the system, ie the kernel, so you can not stop or kill it without killing all of windows. Moreover, the System process is like svchost, that is, it contains multiple items, so you would need to figure out which specific component is the one occupying port 80. The concern is that most of the components that run in the System component tend to be drivers and the like, and as such, have high-level access to the system. A webserver does not need such access, so I would be extremely wary because it sounds like a virus or rootkit is running on the system and is providing a web interface.

You will want to run some security software to check your system for malware.

(From what I can tell, it seems that for some reason, IIS does implant itself in the System instead of a dedicated process like a well behaved program, but if you uninstalled it, then it cannot be the source of the problem. That said, check Services.msc to make sure that IIS is not still present and/or running.)

To find the specific component that is occupying port 80, run Process Explorer and double-click System in the process tree. Look in the Threads tab and sort by Start Address. Now look through the list of drivers and see if any look suspicious. There will be some Windows files as well as driver files for your video, audio, network cards, and such, but you can Google any that do not look familiar. You can check TCPView to monitor any connections to your system.

whyever IIS runs .. it runs as a "service", that is similar to the terminalogy "daemon" on unix. so, neither your malware advice, nor your reference to "it is 'the system'", nor "drivers" etc. IIS is just running on port 80 as a single program and that's all there is. just end that service or launch apache on another port OR bind apache to an ip/interface where IIS is not listening to and thats it. all the rest of your answer has nothing to do with the issue OP has.
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akiraAug 23 '12 at 13:09

This is a horrible answer in 2011, and even a worst answer, now that its 2012..
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RamhoundSep 18 '12 at 14:35